1. Field of the Invention
The present invention relates to a video filming method and apparatus. It has particular use in the filming of a non-uniformly lit scene, such as one lit by a variety of light sources of different intensities or colour temperatures or such as one where certain parts of the scene are shielded from one or more of those light sources.
2. Description of the Related Art
In any scene, there may well be different sources of light, each contributing its own colourisation and intensity to the various areas of the scene. This is true especially of scenes outside the controlled environment of a TV studio.
Typically, the chain of filming equipment comprising cameras, processors, etc is set up to handle only the most critical area of a scene. This has the result that the displayed image may contain colour casts and shading, "burnt-out" areas of highlights, areas of lost detail, etc.
These problems may arise outside, for instance, as a result of bright sunshine, or inside, as illustrated in FIG. 1 of the accompanying drawings.
FIG. 1 illustrates a typical indoor scene. The scene is illuminated by a combination of light sources including daylight, fluorescent tubes and tungsten lamps. Shadows are cast by these mixed sources, resulting in areas of the scene being illuminated to different proportions by the various light sources.
With the illustrated scene, some areas will be illuminated by the high intensity daylight source and others by the lower intensity artificial lamps. This will result in a range of luminance which would be too great to be rendered correctly by a TV camera and system. Furthermore, illumination by daylight will be blue for a camera set for the 3200.degree. K. colour temperature of studio cast and lighting. Similarly, illumination by the fluorescent tubes will influence the colour of the image, since they have a line spectrum output in the range of 2900.degree. K. to 8900.degree. K.
Previously, as illustrated in FIG. 2 of the accompanying drawings, these problems have been dealt with by the use of additional corrective lighting, together with colour and neutral density filters. By correcting the variable light levels and colour temperatures of the mixed sources, a scene may be produced which, when viewed through the television system, will give an acceptable result. In particular, neutral density filters may be placed over the windows to reduce the luminance level of the daylight source, colour correcting filters may be placed over the windows and fluorescent tubes to match the desired colour temperature (fluorescent tubes tend to cause a magenta colour cast), bulbs may be replaced with colour corrected types and, finally, additional lighting may be added to reduce the loss of detail in shadows.
This known method tends to reduce the ambient feel of a set or location. It is also costly as a result of the wide selection of filters required and the significant time needed to set up a correctly balanced scene. Furthermore, this method is not well adapted to reacting to changes in the scene, e.g. resulting from panning of the camera across the scene or daylight changing with time of day or weather conditions.